Method of hardening of photographic films



Patented at so, ?1923.

Parent oar-tea.-

JENS HERMAN CHRISTENSEN, F HOLTE, DENMARK.

METHOD OF HARDENING 0F PHOTOGRAPHIC FILMS.

We Drawing. Application filed November To all whom it may concern:

Be it known that T, J ENS HERMAN CHRIS- TENSEN, a subject of the King ofDenmark, residing at Holte, Denmark, have invented 5 a new and usefulImprovement in Methods of Hardening of Photographic Films; and

I do hereby declare the following to be a full, clear, and exactdescription of the same.

It is well known that" through development of an exposed photographicfilm, containing silver halide and gelatine, by certain developers, forinstance such containing pyrogallol, pyrocatechin, hydrochinon, etc., arelief can be obtained which is due to the fact that the gelatine ishardened in such places in which the development has taken place. Formost practical purposes this hardening, however, is too slight and verymuch inferior to the known hardening by exposure of chromate containinggelatine.

lit has now been proved that this hardening through development can beaugmented in an exceedingly high degree so that it can be compared tothe ohromate hardening and thus can substitute the same in photographicas well as in photomechanical processes, if such provisions are madethat the gelatine during the development is preventedfrom attractingliquid and swelling to any important degree. This is obtained by addingto the developer a suitable very great quantity of such substance whichwill counteract the swelling of the gelatine, for instance alcohol orgreater quantities of salts of poly-basic acids, for instancecarbonates, silicates, etc. Such substances singly or in mixtures, areused as components of generally known developers, but in far smallerquantities. The desired effect, however, will onlyappea-r if thegelatine during the development remains solid and leathery and permitsslow penetration by the developer solution. According to this inventionthese substances therefore are added in such large quantities that thesaid solid, leathery" consistency of the gelatine 'is preserved duringthe development. The followin is an example of the carryin out of theinvention:

The exposed plate is developed ina dark room with a developer consistingof 7 5 parts of alcohol, parts of water, 2 parts of potassium carbonate,p of pyrocatechin, .or alcohol may be le out of the above named formulawhen in return the quan 10, 1919. Serial No. 336,920.

'The development should preferably last several minutes and can beretarded if desired for instance by adding potassium bromide or boricacid 7 A good composition of a developer for finely grained silverbromide plates is for instance the following 180 parts'of water, partsof potassium carbonate, 3 parts of potassium bromide, 1 part ofpyrocatechin, 20 parts of alcohol.

When the development is finished, the plate is rinsed and may if wantedbe fixed, and thereafter it behaves like a chromate hardened gelatine'plate, which is to say for instance. that the non-hardened part may bewashed away with hot' water or be brought to absorb dye solutions sothat the plate can be used as a printing plate.

Specially adapted for this treatment are the socalledsilver-chloride-bromide plates which further have the advantage of beingsensitive to light of difi'erent colors and easily controllable duringthe development as the sensitiveness is not very great.

Such silver chloride-bromide plates there fore are adapted for theproduction of printing plates forv three color prints.

The said printing plates may be flexible, the film being arranged on acarrier of celluloid or metal and they may have a suitable perforationin order to facilitate the registering during the exposure and printing.

Having thus fully described my invention .1 claim as new and desire tosecure by Letters Patent:

1. The method of developing photographic plates or films to provide apicture of hardened gelatine which consists in treat- Q emmas graphicplates or films to provide a picture In testimony whereof I have aflixedmy of haidened gelatine which consists in treatsignature in presence oftwo Witnesses.

ing t e exposed and undeveloped plate or v film with pyrocatechi'n and amixture of TENS HERMAN CHRISTENSEN 5 alcohol and .a substance selectedfrom the Witnesses:

group consisting of potassium carbonate CECIL V. ScHoN, and potassiumbromide. VIGGO BLoM.

